This invention relates to tracking error control apparatus for use in h signal reproducing system and, more particularly, to such apparatus for correcting tracking errors that may arise when a record medium from which signals are reproduced is moved relative to one or more rotary transducers at a speed that differs from the speed thereof at which such signals originally were recorded.
In rotary head recording/reproducing systems, signals can be recorded with relatively high density over a relatively wide frequency spectrum in a series of parallel tracks on a movable record medium. Typical of such recording/reproducing systems is the video tape recorder (VTR) in which video signals are recorded in parallel, skewed record tracks along a moving magnetic tape. In a typical VTR, one or more heads serves as a recording head and also as a reproducing head; and such head or heads is rotated at a substantially constant speed for both recording and reproducing operations. If the speed at which the magnetic tape moves during a reproducing operation is identical to the speed at which the tape was moved during a recording operation, then each scanning trace of the reproducing head easily can be made to coincide with each previously recorded record track. However, such coincidence is not readily obtained if the tape is moved at a slower or faster speed during the reproducing operation. That is, if the ratio between the tape reproducing speed and the tape recording speed is N, then a tracking error will occur when N.noteq.1.
In the aforementioned reproducing mode wherein N.noteq.1, the scanning traces of each reproducing head will be parallel to each other, but such traces will not be parallel to the record tracks on the magnetic tape. For example, if N&lt;1, the angle which each scanning trace makes with respect to the longitudinal axis of the tape is smaller than the angle which each record track makes with this longitudinal axis. Furthermore, when N&lt;1, a plurality of scanning traces may be formed across the tape, whereas only a single record track is recorded. Each of these traces exhibits a deviation, or tracking error, with respect to the particular record track which is being scanned.
In order to overcome this problem, a so-called displaceable support member has been developed for each reproducing head. The displaceable support member may be an electrostriction device, such as a piezoceramic element known, for example, as a bi-morph leaf assembly. Typically, a bi-morph leaf assembly is responsive to control signals to deflect by an amount that is determined by such control signals. It is appreciated that if a head is mounted upon such a bi-morph leaf assembly, the deflection of the assembly will result in a displacement of the head. It has been proposed, heretofore, to arrange the bi-morph leaf assembly such that, as the reproducing head is rotated, control signals applied to the bi-morph leaf assembly will result in a corresponding displacement of the head in a direction which is transverse to the scanning trace. Consequently, even if the scanning trace of the head crosses, or intersects, a record track, compensating control signals can be applied to the bi-morph leaf assembly such that the head is displaced in a direction to bring it into coincidence with that record track.
When N.noteq.1, the compensating drive signal which must be supplied to the bi-morph leaf assembly to eliminate the head tracking error generally is of a sawtooth waveform. If a plurality of traces are formed for each record track, as is the case when N&lt;1, each trace must be shifted by a respective, constant amount in addition to being continuously adjusted for coincidence with the record track. This means that, in addition to the sawtooth waveform which is used as a compensating drive signal for the bi-morph leaf assembly, a staircase waveform compensating drive signal also must be supplied thereto. Both the sawtooth waveform and the staircase waveform have parameters which are dependent upon the actual speed at which the tape is moved. For the proper compensation of tracking errors, the apparatus which is used to produce the compensating drive signals must, therefore, take the actual tape speed into account.